In order to know the current global carbon cycle,it is necessary to examine temporal and spatial variations in air-sea CO2 flux.We have reported the seasonal variation and the long-term trend of pCO2 sea in the western North Pacific Subtropical Gyre (NPSG) and the western equatorial Pacific [Inoue et al.,1995; Midorikawa et al.,2005].The western NPSG acts as a sink for atmospheric CO2 and the western equatorial Pacific as a weak source.In the western NPSG,seasonal variations in pCO2 sea are mainly controlled by variations in sea surface temperature (SST),the biological activities,and ocean dynamics.We reported that factors controlling carbonate system in the subtropics (between Hawaii and Japan) are seasonally variable.At the moment,however,to what extent these factors contributed to the air-sea CO2 flux is poorly understood in the wide area of the western North Pacific.Based on the pCO2 sea and pCO2 air data in the western North Pacific,we report the seasonal,inter-annual and the long-term trend of air-sea CO2 flux in the western North Pacific over the period from 1990 to 2004.